One of the principal problems encountered during use of wave soldering machines is the oxidation of the liquid solder bath, this oxidation creating on the surface of the bath a film or oxide slag which can substantially alter the brazing or tinning of the components and which increases the cost of production. The first solution to reduce the formation of slag on the surface of the solder bath consists in associating with the soldering tank a hood enclosing at least the bath and containing an inert gas, typically nitrogen, constituting the gaseous overhead with the bath. Such a technique is described for example in French application No. 90.15994 in the name of the applicant, whose content is incorporated herein by reference. Although such techniques permit substantially reducing the oxidation of the solder bath, the oxygen content cannot as a practical matter, because of leakage and entry of air on the pass of the component, be reduced to extremely low values, of the order of ppm.